Psycho killerFlickrHumans think of cats as fuzzy and cute. Birds and small mammals have a vastly different perception.

Domestic cats kill between 1.4 and 3.7 billion birds and between 6.9 and 20.7 billion mammals (mostly mice, shrews, rabbits, squirrels and voles) each year, according to a new study published Tuesday, Jan. 29, in Nature Communications.

Both stray and owned cats are responsible for a far greater number of bird and mammal deaths in the contiguous United States than previously estimated, outpacing other threats such as collisions with windows, buildings, communication towers, cars and poisoning, the report notes.

Free-ranging cats are "likely the single greatest source of anthropogenic (man-made) mortality for US birds and mammals," according to the report.

Un-owned cats (farm cats, feral cats, and stray cats that are fed by humans, for example) are the main perpetrators, but owned cats do their fair share of killing, too.

Researchers guess that a single cat may kill between 100 and 200 mammals annually, meaning a population estimate of between 30 and 80 million un-owned cats would result in the death of 3 and 8 billion mammals, if you were to look at the low-end kill estimate. And that's just un-owned cats. The researchers calculated around 84 million owned cats, the majority of which are allowed outdoors.

"The magnitude of our mortality estimates suggest that cats are likely causing population declines for some species and in some regions," the study authors write.

The timing of the study is uncanny. Just last week, a prominent New Zealand economist upset the international cat community when he called for the eradication of cats, citing their threat to the country's unique wildlife.

Meanwhile, the study authors are critical of current tactics to control feral cat populations, including Trap-Neuter-Return, a project aimed at capturing and sterilizing feral cats.

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